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Discussion Starter #1
I picked up a 1987 Polaris Indy Trail 440 fan to bomb around with the kids. Problem is that it backfires when I hit over 6000 rpm's like a pop, pop, pop. seems to bog a little at the same time but still has some power. I am not familiar working on sleds but can do stuff myself. So far I replaced the plugs, took the carb's apart and cleaned them. It iddled high and adjusted it down to about 2000 rpm. If the track if off the ground it does not really backfire but when I am on it, clutch engages around 4000 rpm and coasting at 5000 rpm's I am not moving fast but it is ok. Give it gas to over 6000 rpm's and she backfires like a sputter. Any clue as to what I should check?
 

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Discussion Starter #2
Anyone have a clue or recommendations?

Also I noticed the primary clutch does not really compress together when engaged, would this have something to do with it or is this a separate problem altogether?
 

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Couple of things to try...Backfiring is sometimes caused by a lean condition. Check the crank seals by spraying a little carb cleaner around them and pay attention to the idle speed. If it changes up or down there's a chance that the seals are bad. Clean the carbs! There are 3 fuel circuits in the carbs and a little garbage in any one of them can hose up the mixture . Also, check the ignition wires and coils...spray the wires with water or windex and run the engine in the dark. If there is any arcing between the wires or coils then you need to change those parts out.
Will the engine rev above 6000 or does it just backfire and lose power completely at that point?
 

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Discussion Starter #4
It will rev above 6000, I was at near 7000 and it seems to want to have power but it just backfires more.

I had the carbs off last week and soaked them for a 2 hours in solvent and had tried as well as adding Seanfoam in the gas. Yesterday I took the carbs off and took them apart and cleaned them out with Carb cleaner and re-installed. I ressearched the setting for the air screw as I did not know if it was set properly and set it at 1 1/4 turn from snug position. Seems like the plugs are burning properly.

I will try the ingnition wires and coil as well as the crank seals.
 

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Discussion Starter #5
I checked the wires and coil for arcing and did not see anything. As for the crank seals I pressume this is located behind the primary cluth? If so that is where I sprayed carb cleaner and did not notice any difference in rpm.

The more I read other post, I am thinking it has to be carb???? Not sure.

I did notice that it does the same conditions when I have the track in the air unlike what I had stated earlier. I had it up today and decided I would pin it and hold it to see what it would do. The belt on the primary cluth rose to the top as it should and I was looking at the rpm's, they where at 7000-8000 and sounded like it had the power and I could here it back firing. I removed the plugs and the one on the exhaust side was a little wet and a little dark, had a little smoke coming out of the hole. Other side was burning properly, dry and cardboard color. Earlier when I had checked the plugs they where both the same cardboard color and dry.

Not sure if I should take the carb apart again? This was the first time I took a carb apart, maybe I did not do it properly?
 

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I had this same problem with my xlt last week one plug black and wet looking and the other two a nice brown. I checked everything twice and would still do it finally changed the plugs and it runs fine try that before you tear it apart again
 
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